3 research outputs found
Tridentate Benzimidazole-Pyridine-Tetrazolates as Sensitizers of Europium Luminescence
We report on new anionic tridentate
benzimidazole-pyridine-tetrazolate ligands that form neutral 3:1 complexes
with trivalent lanthanides. The ligands are UV-absorbing chromophores
that sensitize the red luminescence of europium with energy-transfer
efficiency of 74–100%. The lifetime and quantum yield of the
sensitized europium luminescence increase from 0.5 ms and 12–13%
for the as-prepared solids to 2.8 ms and 41% for dichloromethane solution.
From analysis of the data, the as-prepared solids can be described
as aqua-complexes [LnÂ(κ<sup>3</sup>-ligand)<sub>2</sub>(κ<sup>1</sup>-ligand)Â(H<sub>2</sub>O)<sub><i>x</i></sub>] where
the coordinated water molecules are responsible for the strong quenching
of the europium luminescence. In solution, the coordinated water molecules
are replaced by the nitrogen atoms of the κ<sup>1</sup>-ligand
to give anhydrous complexes [LnÂ(κ<sup>3</sup>-ligand)<sub>3</sub>] that exhibit efficient europium luminescence. X-ray structures
of the anhydrous complexes confirm that the lanthanide ion (La<sup>III</sup>, Eu<sup>III</sup>) is nine-coordinate in a distorted tricapped
trigonal prismatic environment and that coordination of the lanthanide
ion by tetrazolate is weaker than by carboxylate
Tridentate Benzimidazole-Pyridine-Tetrazolates as Sensitizers of Europium Luminescence
We report on new anionic tridentate
benzimidazole-pyridine-tetrazolate ligands that form neutral 3:1 complexes
with trivalent lanthanides. The ligands are UV-absorbing chromophores
that sensitize the red luminescence of europium with energy-transfer
efficiency of 74–100%. The lifetime and quantum yield of the
sensitized europium luminescence increase from 0.5 ms and 12–13%
for the as-prepared solids to 2.8 ms and 41% for dichloromethane solution.
From analysis of the data, the as-prepared solids can be described
as aqua-complexes [LnÂ(κ<sup>3</sup>-ligand)<sub>2</sub>(κ<sup>1</sup>-ligand)Â(H<sub>2</sub>O)<sub><i>x</i></sub>] where
the coordinated water molecules are responsible for the strong quenching
of the europium luminescence. In solution, the coordinated water molecules
are replaced by the nitrogen atoms of the κ<sup>1</sup>-ligand
to give anhydrous complexes [LnÂ(κ<sup>3</sup>-ligand)<sub>3</sub>] that exhibit efficient europium luminescence. X-ray structures
of the anhydrous complexes confirm that the lanthanide ion (La<sup>III</sup>, Eu<sup>III</sup>) is nine-coordinate in a distorted tricapped
trigonal prismatic environment and that coordination of the lanthanide
ion by tetrazolate is weaker than by carboxylate
A Eu<sup>III</sup> Tetrakis(β-diketonate) Dimeric Complex: Photophysical Properties, Structural Elucidation by Sparkle/AM1 Calculations, and Doping into PMMA Films and Nanowires
Reaction of Ln<sup>III</sup> with
a tetrakisÂ(diketone) ligand H<sub>4</sub>L [1,1′-(4,4′-(2,2-bisÂ((4-(4,4,4-trifluoro-3-oxobutanoyl)
phenoxy)Âmethyl)Âpropane-1,3-diyl)ÂbisÂ(oxy)ÂbisÂ(4,1-phenylene))ÂbisÂ(4,4,4-trifluorobutane-1,3-dione)]
gives new podates which, according to mass spectral data and Sparkle/AM1
calculations, can be described as dimers, (NBu<sub>4</sub>[LnL])<sub>2</sub> (Ln = Eu, Tb, Gd:Eu), in both solid-state and dimethylformamide
(DMF) solution. The photophysical properties of the Eu<sup>III</sup> podate are compared with those of the mononuclear diketonate (NBu<sub>4</sub>[EuÂ(BTFA)<sub>4</sub>], BTFA = benzoyltrifluoroacetonate),
the crystal structure of which is also reported. The new Eu<sup>III</sup> dimeric complex displays bright red luminescence upon irradiation
at the ligand-centered band in the range of 250–400 nm, irrespective
of the medium. The emission quantum yields and the luminescence lifetimes
of (NBu<sub>4</sub>[EuL])<sub>2</sub> (solid state: 51% ± 8%
and 710 ± 2 μs; DMF: 31% ± 5% and 717 ± 1 μs)
at room temperature are comparable to those obtained for NBu<sub>4</sub>[EuÂ(BTFA)<sub>4</sub>] (solid state: 60 ± 9% and 730 ±
5 μs; DMF: 30 ± 5% and 636 ± 1 μs). Sparkle/AM1
calculations were utilized for predicting the ground-state geometries
of the Eu<sup>III</sup> dimer. Theoretical Judd–Ofelt and photoluminescence
parameters, including quantum yields, predicted from this model are
in good agreement with the experimental values, proving the efficiency
of this theoretical approach implemented in the LUMPAC software (http://lumpac.pro.br). The kinetic scheme for modeling energy
transfer processes show that the main donor state is the ligand triplet
state and that energy transfer occurs on both the <sup>5</sup>D<sub>1</sub> (44.2%) and <sup>5</sup>D<sub>0</sub> (55.8%) levels. Furthermore,
the newly obtained Eu<sup>III</sup> complex was doped into a PMMA
matrix to form highly luminescent films and one-dimensional nanowires
having emission quantum yield as high as 67%–69% (doping concentration
= 4% by weight); these materials display bright red luminescence even
under sunlight, so that interesting photonic applications can be foreseen